The Class of Fishes is divided into four sub-classes:—

I. Palæichthyes.—Heart with a contractile conus arteriosus; intestine with a spiral valve; optic nerves non-decussating, or only partially decussating.

II. Teleostei.—Heart with a non-contractile bulbus arteriosus; intestine without spiral valve; optic nerves decussating. Skeleton ossified, with completely separated vertebræ.

III. Cyclostomata.—Heart without bulbus arteriosus; intestine simple. Skeleton cartilaginous and notochordal. One nasal aperture only. No jaws; mouth surrounded by a circular lip.

IV. Leptocardii.—Heart replaced by pulsating sinuses; intestine simple. Skeleton membrano-cartilaginous and notochordal. No skull; no brain.

FIRST SUB-CLASS: PALÆICHTHYES.

Heart with a contractile conus arteriosus;[30] intestine with a spiral valve;[31] optic nerves non-decussating, or only partially decussating;[32] skeleton cartilaginous or osseous.

This sub-class comprises the Sharks and Rays, and the Ganoid fishes. Although based upon a singular concurrence of most important characters, its members exhibit as great a diversity of form, and as manifold modifications in the remainder of their organisation as the Teleostei. The Palæichthyes stand to the Teleostei in the same relation as the Marsupials to the Placentalia. Geologically, as a sub-class, they were the predecessors of Teleosteous fishes; and it is a remarkable fact that all those modifications which show an approach of the ichthyic type to the Batrachians are found in this sub-class. We divide it into two orders: Chondropterygii and Ganoidei.

FIRST ORDER: CHONDROPTERYGII.

Skeleton cartilaginous. Body with medial and paired fins, the hinder pair abdominal. Vertebral column generally heterocercal, the upper lobe of the caudal fin produced. Gills attached to the skin by the outer margin, with several intervening gill-openings: rarely one external gill-opening only. No gill-cover. No air-bladder. Two, three, or more series of valves in the conus arteriosus. Ova large and few in number,[33] impregnated and, in some species, developed within a uterine cavity. Embryo with deciduous external gills.[34] Males with intromittent organs attached to the ventral fins.[35]

This order, for which, also, the name Elasmobranchii has been proposed (by Bonaparte), comprises the Sharks and Rays and Chimæras, and is divided into two suborders: Plagiostomata and Holocephala.

FIRST SUB-ORDER: PLAGIOSTOMATA.

From five to seven gill-openings. Skull with a suspensorium and the palatal apparatus detached. Teeth numerous.

The Plagiostomes differ greatly among each other with regard to the general form of their body: in the Sharks or Selachoidei the body is elongate, more or less cylindrical, gradually passing into the tail; their gill-openings are lateral. In the Rays, or Batoidei, the gill-openings are always placed on the abdominal aspect of the fish; the body is depressed, and the trunk, which is surrounded by the immensely developed pectoral fins, forms a broad flat disk, of which the tail appears as a thin and slender appendage. Spiracles are always present; the number of gill-openings is constantly five; no anal fin; dorsal fins, if present, situated on the tail. However, some of the Rays approach the Sharks in having the caudal portion less abruptly contracted behind the trunk.

Fossil Plagiostomes are very numerous in all formations. Some of the earliest determinable fish remains are believed to be, or are, derived from Plagiostomes. Those which can be referred to any of the following families will be mentioned subsequently: but there are others, especially fin-spines, which leave us in doubt to which group of Plagiostomes their owners had any affinity, thus Onchus from the upper Silurian, continuing to carboniferous formations; Dimeracanthus, Homocanthus, from the Devonian; Oracanthus, Gyracanthus, Tristychius, Astroptychius, Ptychacanthus, Sphenacanthus, etc., from carboniferous formations; Leptacanthus, from the coal to the Oolite; Cladacanthus, Cricacanthus, Gyropristis, and Lepracanthus, from the coal measures; Nemacanthus, Liacanthus, from the Trias; Astracanthus, Myriacanthus, Pristacanthus, from the Jurassic group.

A. Selachoidei: Sharks.

The elongate cylindrical body, generally terminating in a more or less pointed snout, and passing into a powerful and flexible tail, blade-like at its extremity, gives to the Sharks a most extraordinary power of swimming, with regard to endurance as well as rapidity of motion. Many, especially the larger kinds, inhabit the open ocean, following ships for weeks, or pursuing shoals of fishes in their periodical migrations. Other large-sized sharks frequent such parts of the coast as offer them abundance of food; whilst the majority of the smaller kinds are shore fishes, rarely leaving the bottom, and sometimes congregating in immense numbers. The movements of sharks resemble in some measure those of snakes, their flexible body being bent in more than one curve when moving.

Sharks are most numerous in the seas between the Tropics, and become scarcer beyond, a few only reaching the Arctic circle; it is not known how far they advance southwards towards the Antarctic region. Some species enter fresh waters, and ascend large rivers, like the Tigris or Ganges, to a considerable distance. The pelagic as well as the shore species have a wide geographical range. Very few descend to a considerable depth, probably not exceeding 500 fathoms. There are about 140 different species known.

Sharks have no scales like those of other fishes; their integuments are covered with calcified papillæ which, under the microscope, show a structure similar to that of teeth. If the papillæ are small, pointed, and close set, the skin is called “shagreen;” rarely they are larger, appearing as bucklers or spines, of various sizes.

These fishes are exclusively carnivorous, and those armed with powerful cutting teeth are the most formidable tyrants of the ocean. They have been known to divide the body of a man in two at one bite, as if by the sweep of a sword. Some of the largest sharks, however, which are provided with very small teeth, are almost harmless, feeding on small fishes only or marine invertebrates. Others, particularly of the smaller kinds, commonly called “Dog-fishes,” have short or obtuse teeth, and feed on shells or any other animal substance. Sharks scent their food from a distance, being readily attracted by the smell of blood or decomposing bodies.

In China and Japan, and many other eastern countries, the smaller kinds of sharks are eaten. Sharks’ fins form in India and China a very important article of trade, the Chinese preparing from them gelatine, and using the better sorts for culinary purposes. The fins are obtained not exclusively from Sharks but also from Rays, and assorted in two kinds, viz. “white and black.” The white consist exclusively of the dorsal fins, which are on both sides of the same uniform light colour, and reputed to yield more gelatine than the other fins. The pectoral, ventral, and anal fins pass under the denomination of black fins; the caudal fin is not used. One of the principal places where shark fishery is practised as a profession is Kurrachee. Dr. Buist, writing in 1850 (“Proc. Zool. Soc.” 1850, p. 100), states that there are thirteen large boats, with crews of twelve men each, constantly employed in this pursuit; that the value of the fins sent to the market varies from 15,000 to 18,000 rupees; that one boat will sometimes capture at a draught as many as one hundred sharks of various sizes; and that the number total of sharks captured during the year amounts probably to not less than 40,000. Large quantities are imported from the African coast and the Arabian Gulf, and various ports on the coast of India. In the year 1845–46, 8770 cwt. of sharks’ fins were exported from Bombay to China.

First Family—Carchariidæ.

Eye with a nictitating membrane. Mouth crescent-shaped, inferior. Anal fin present. Two dorsal fins, the first opposite to the space between pectoral and ventral fins, without spine in front.

This genus comprises the true Sharks, common in the tropical, but less so in the temperate seas. Between thirty and forty different species have been distinguished, of which one of the most common is the “Blue Shark” (Carcharias glaucus). Individuals of from twelve to fifteen feet are of very common occurrence, but some of the species attain a much larger size, and a length of 25 and more feet. Fishes of this genus or of closely allied genera (Corax, Hemipristis) are not uncommon in the chalk and tertiary formations.

Three species, of which one (G. arcticus) is confined to the arctic and sub-arctic oceans. The others inhabit temperate and tropical seas, and all attain to a very large size.

These are small sharks, commonly called “Tope.” The species found on the British coast is spread over nearly all the temperate and tropical seas, and is common in California and Tasmania. It lives on the bottom, and is very troublesome to fishermen by constantly taking away bait or driving away the fishes which they desire to catch.

The “Hammerheads,” or Hammerheaded Sharks, have a dentition very similar to that of Carcharias, and although they do not attain to the same large size, they belong to the most formidable fishes of the ocean. The peculiar form of their head is quite unique among fishes; young examples have the lateral extension of the skull much less developed than adults. Five species are known, which are most abundant in the tropics. By far the most common is Zygæna malleus, which occurs in nearly all tropical and sub-tropical seas. Specimens of this species may be often seen ascending from the clear blue depths of the ocean like a great cloud. Cantor found in a female, nearly 11 feet long, thirty-seven embryons.—Hammerheads have lived from the cretaceous epoch.

The “Hounds” are small Sharks, abundant on the coasts of all the temperate and tropical seas; two of the five species known occur on the coasts of Europe, viz. M. lævis and M. vulgaris. Closely allied as these two species are, they yet show a most singular difference, viz. that a placenta is developed in the uterus for the attachment of the embryo in M. lævis (the Γαλεὁς λεȋος of Aristotle, to whom this fact was already known); whilst the embryons of M. vulgaris are developed without such placenta (see J. Müller, “Abhandl. Ak. Wiss.” Berl. 1840). The Hounds are bottom fish, which feed principally on shells, crustaceans, and decomposing animal substances.

Several other genera belong to the family Carchariidæ, but it will be sufficient to mention their names:—Hemigaleus, Loxodon, Thalassorhinus, Triænodon, Leptocarcharias, and Triacis.

Second Family—Lamnidæ.

Eye without nictitating membrane. Anal fin present. Two dorsal fins; the first opposite to the space between pectoral and ventral fins, without spine in front. Nostrils not confluent with the mouth which is inferior. Spiracles absent or minute.

All the fishes of this family attain to a very large size, and are pelagic. But little is known of their reproduction. The first appearance of this family is indicated by Carcharopsis, a genus from carboniferous formations, the teeth of which differ from those of Carcharodon only by having a broad fold at the base. In the chalk and tertiary formations almost all the existing genera are represented; and, besides, Oxytes, Sphenodus, Gomphodus, and Ancistrodon, which are known from teeth only, have been considered generically distinct from the living Porbeagles.

Of the “Porbeagles,” three species have been described, of which the one occurring in the North Atlantic, and frequently straying to the British coasts (L. cornubica), is best known. It attains to a length of ten feet, and feeds chiefly on fishes; its lanceolate teeth are not adapted for cutting, but rather for seizing and holding its prey, which it appears to swallow whole. According to Pennant it is viviparous; only two embryoes were found in the female which came under his observation. Haast has found this species also off the coast of New Zealand.

One species only is known (C. rondeletii), which is the most formidable of all Sharks. It is strictly pelagic; and appears to occur in all tropical and sub-tropical seas. It is known to attain to a length of 40 feet. The tooth figured here, of the natural size, is taken from a jaw 20 inches wide in its transverse diameter (inside measure), each half of the mandible measuring 22 inches.[36] The whole length of the fish was 36½ feet.

Carcharodon teeth are of very common occurrence in various tertiary strata, and have been referred to several species, affording ample evidence that this type was much more numerously represented in that geological epoch than in the recent fauna. Some individuals attained to an immense size, as we may judge from teeth found in the Crag, which are 4 inches wide at the base, and 5 inches long, measured along their lateral margin. The naturalists of the “Challenger” expedition have made the highly interesting discovery that teeth of similar size are of common occurrence in the ooze of the Pacific, between Polynesia and the west coast of America. As we have no record of living individuals of that bulk having been observed, the gigantic species to which these teeth belonged must have become extinct within a comparatively recent period. Nothing is known of the anatomy, habits, and reproduction of the surviving species, and no opportunity should be lost of obtaining information on this Shark.

Large Sharks from tropical and temperate seas; two species.

This genus consists of one species only, which is known by the name of “Fox-shark” or “Thresher.” It is the most common of the larger kinds of Sharks which occur on the British coasts; and seems to be equally common in other parts of the Atlantic and Mediterranean, as well as on the coasts of California and New Zealand. It attains to a length of fifteen feet, of which the tail takes more than one half; and is quite harmless to man. It follows the shoals of Herrings, Pilchards, and Sprats in their migrations, destroying incredible numbers. When feeding it uses the long tail in splashing the surface of the water, whilst it swims in gradually decreasing circles round a shoal of fishes, which are thus kept crowded together, falling an easy prey to their enemy. Statements that it has been seen to attack Whales and other large Cetaceans, rest upon erroneous observations.

Also this genus consists of one species only, the “Basking Shark” (Pélerin of the French). It is the largest Shark of the North Atlantic, growing to a length of more than thirty feet. It is quite harmless if not attacked; its food consisting of small fishes, and other small marine animals swimming in shoals. On the west coast of Ireland it is chased for the sake of the oil which is extracted from the liver, one fish yielding from a ton to a ton and a-half. Its capture is not unattended with danger, as one blow from the enormously strong tail is sufficient to stave in the sides of a large boat. At certain seasons it is gregarious, and many specimens may be seen in calm weather lying together motionless, with the upper part of the back raised above the surface of the water; a habit from which this Shark has derived its name. The buccal and branchial cavities are of extraordinary width, and, in consequence of the flabby condition of those parts, the head presents a variable and singular appearance in specimens lying dead on the ground. This peculiarity, as well as the circumstance that young specimens have a much longer and more pointed snout than adult ones, has led to the erroneous opinion that several different genera and species of Basking Shark occur in the European seas. The branchial arches of Selache are provided with a very broad fringe of long (five to six inches) and thin gill-rakers, possessing the same microscopical structure as the teeth and dermal productions of Sharks. Similar gill-rakers have been found in a fossil state in the Crag of Anvers in Belgium, proving the existence of this Selachian type in the tertiary epoch. Nothing is known of the reproduction of this fish. The latest contributions to its history are by Steenstrup in “Overs. Dansk. Vidensk. Selsk., Forhandl.” 1873, and by Pavesi in “Annal. Mus. Civ. Geneva,” 1874 and 1878.

Third Family—Rhinodontidæ.

No nictitating membrane. Anal fin present. Two dorsal fins, the first nearly opposite to the ventrals, without spine in front. Mouth and nostril near the extremity of the snout.

This small family comprises one species only, Rhinodon typicus, a gigantic Shark, which is known to exceed a length of fifty feet, but is stated to attain that of seventy. It does not appear to be rare in the western parts of the Indian Ocean, and possibly occurs also in the Pacific. It is one of the most interesting forms, not unlike the Basking Shark of the Northern Seas, having gill-rakers like that species; but very little is known of its structure and mode of life. It is perfectly harmless, its teeth being extremely small and numerous, placed in broad bands; it has been stated to feed on tang, an observation which requires confirmation. The snout is very broad, short, and flat; the eyes are very small. A pit at the root of the caudal fin which has the lower lobe well developed; side of the tail with a keel. A characteristic figure of this fish has been given by A. Smith in his “Illustrations of the Zoology of South Africa,” Plate 26, from a specimen which came ashore at the Cape of Good Hope.

Fourth Family—Notidanidæ.

No nictitating membrane. One dorsal fin only, without spine, opposite to the anal.

Four species are known, distributed over nearly all the tropical and sub-tropical seas; they attain to a length of about fifteen feet. Fossil teeth belonging to this type have been found in Jurassic and later formations (Notidanus and Aellopos).

Fifth Family—Scylliidæ.

Two dorsal fins, without spine: the first above or behind the ventrals; anal fin present. No nictitating membrane. Spiracle always distinct. Mouth inferior. Teeth small, several series generally being in function.

The fishes of this genus are of small size, and commonly called “Dog-fishes.” They are coast fishes, living on the bottom, and feeding on Crustaceans, dead fishes, etc. None of the eight species known have a very wide distribution, but where they occur they are generally sufficiently abundant to prove troublesome to fishermen. They inhabit most parts of the temperate and tropical seas. On the British coasts two species are found, the “Larger” and “Lesser spotted Dog-fish,” Scyllium canicula and Scyllium catulus, which are said to be more plentiful among the Orkney Islands than elsewhere. They are scarcely ever brought to market; but the fishermen of some localities do not disdain to eat them. Their flesh is remarkably white, a little fibrous, and dry. In the Orkneys they are skinned, split up, cleaned, and then spread out on the rocks to dry for home consumption. The skins are used for smoothing down cabinet-work. It would be worth while to apply the fins of these and other Sharks, which are so extensively used in China for making gelatine soups, to the same purpose in this country, or to dry them for exportation to the East. Most of the species of Dog-fishes are spotted, and those of the allied genera, Parascyllium and Chiloscyllium, very handsomely ornamented.

Closely allied to Scyllium is Pristiurus, from the coasts of Europe, which is provided with a series of small flat spines on each side of the upper edge of the caudal fin.

Fossil forms of Dog-fishes are not scarce in the Lias and Chalk: Scylliodus, Palæoscyllium, Thyellina, Pristiurus.

Four species from the tropical parts of the Atlantic and Indian Oceans, attaining to a length of some 12 feet. Pelagic.

The single species (St. tigrinum) for which this genus has been formed, is one of the commonest and handsomest sharks of the Indian Ocean. Young individuals keep generally close to the coasts, whilst the adult, which are from 10 to 15 feet long, are not rarely met in the open ocean. The colour is a brownish yellow, ornamented with black or brown transverse bands, or with snuff-coloured rounded spots; hence this shark is frequently mentioned by the names of “Zebra-Shark” or “Tiger-Shark.”

“Dog-fishes,” from the Indian Ocean, of small size. Four species are known, of which one, Ch. indicum, is one of the commonest shore-fishes on the coasts of this region, extending from the southern extremity of the African Continent to Japan.

Three species are known from the Australian and Japanese coasts. They are evidently ground-sharks, which lie concealed on the bottom watching for their prey. In accordance with this habit their colour closely assimilates that of a rock or stone covered with short vegetable and coralline growth—a resemblance increased by the frond-like tentacles on the side of the head. This peculiarity of the integuments, which is developed in a yet higher degree in Pediculati and Lophobranchs, is not met with in any other Selachian. These Sharks grow to a length of 10 feet.

Sixth Family—Hybodontidæ.

Two dorsal fins, each with a serrated spine. Teeth rounded, longitudinally striated, with one larger, and from two to four smaller lateral cusps. Skin covered with shagreen.

Extinct. From carboniferous, liassic, and triassic formations. Several genera have been distinguished; and if Cladodus belongs to this family, it would have been represented even in the Devonian.

Seventh Family—Cestraciontidæ.

No nictitating membrane. Two dorsal fins, the first opposite to the space between pectoral and ventral fins; anal fin present. Nasal and buccal cavities confluent. Teeth obtuse, several series being in function.

This family is one of particular interest, because representatives of it occur in numerous modifications in primary and secondary strata. Their dentition is uniformly adapted for the prehension and mastication of crustaceous and hard-shelled animals. The fossil forms far exceeded in size the species of the only surviving genus; they make, their appearance with Ctenoptychius in the Devonian; this is succeeded in the coal-measures by Psammodus, Chomatodus, Petrodus, Cochliodus, Polyrhizodus, etc.; in the Trias and Chalk by Strophodus, Acrodus, Thectodus, and Ptychodus. Of the 25 genera known, 22 have lived in the periods preceding the Oolitic.

Four species are known from Japan, Amboyna, Australia, the Galapagoes Islands, and California; none exceed a length of 5 feet. The egg has been figured on p. 168 (Fig. 80).

Eighth Family—Spinacidæ.

No membrana nictitans. Two dorsal fins; no anal. Mouth but slightly arched; a long, deep, straight, oblique groove on each side of the mouth. Spiracles present; gill-openings narrow. Pectoral fins not notched at their origin.

The oldest representative of this family (Palæospinax) occurs at Lyme Regis; its skin is granular; each dorsal fin possesses a spine; the teeth in the jaws are dissimilar—the upper being multicuspid, longitudinally ribbed as in Hybodus, the lower smooth and tricuspid. Drepanophorus and Spinax primævus occur in Cretaceous formations of England and the Lebanon.

One species, Centrina salviani, from the Mediterranean and neighbouring parts of the Atlantic; of small size.

The two species of “Spiny Dog-fishes,” A. vulgaris and A. blainvillii, have a very remarkable distribution, being found in the temperate seas of the Northern and Southern Hemispheres, but not in the intermediate tropical zone. They are of small size, but occur at times in incredible numbers, 20,000 having been taken in one scene on the Cornish coast. They do much injury to the fishermen by cutting their lines and carrying off their hooks.

Eight species are known from the southern parts of the European seas, and one from the Moluccas; they do not appear to exceed a length of five feet. According to the observations of E. P. Wright, some of the species at least live at a considerable depth, perhaps at a greater depth than any of the other known Sharks. The Portuguese fishermen fish for them in 400 or 500 fathoms with a line of some 600 fathoms in length. The Sharks caught were specimens of Centrophorus coelolepis, from three to four feet long. “These sharks, as they were hauled into the boat, fell down into it like so many dead pigs; there was not the smallest motion of their bodies. There can be no reasonable doubt that they were inhabitants of the same great depth as Hyalonema” and that, in fact, they were killed by being dragged to the surface from the pressure of water under which they lived. The dermal productions of some of the species have a very peculiar form, being leaf-shaped, pedunculate, or ribbed, or provided with an impression.

Three small species from the Atlantic and the southern extremity of America. Centroscyllium is an allied genus from the coast of Greenland.

A single species, S. lichia, is rather common in the Mediterranean and the neighbouring parts of the Atlantic.

The “Greenland Shark” is an inhabitant of the Arctic regions, but rarely straying to the latitudes of great Britain; it grows to a length of about 15 feet, and, although it never or but rarely attacks man, is one of the greatest enemies of the whale, which is often found with large pieces bitten out of the tail by this Shark. Its voracity is so great that, according to Scoresby, it is absolutely fearless of the presence of man whilst engaged in feeding on the carcass of a whale, so that it can be pierced through with a spear or knife without being driven away. It is stated to be viviparous, and to produce about four young at a birth.

The “Spinous Shark” is readily recognised by the short bulky form of its body, short tail, and large spinous tubercles. It is evidently a ground-shark, which probably lives at some depth and but accidentally comes to the surface. More frequently met with in the Mediterranean, it has been found several times on the south coast of England, and near the Cape of Good Hope.

Euprotomicrus and Isistius are two other genera of this family; they are pelagic and but little known.

Ninth Family—Rhinidæ.

No anal fin; two dorsal fins. Spiracles present. Pectoral fins large, with the basal portion prolonged forwards, but not grown to the head.

The “Angel-fish,” or “Monk-fish” (Rh. squatina), approaches the Rays as regards general form and habits. Within the temperate and tropical zones it is almost cosmopolitan, being well known on the coasts of Europe, eastern North America, California, Japan, South Australia, etc.; it does not seem to exceed a length of five feet; it is viviparous, producing about twenty young at a birth.

Extinct forms, closely allied to the “Angel-fish,” are found in the Oolite, and have been described as Thaumas. The carboniferous genus, Orthacanthus, may have been allied to this family, but it was armed with a spine immediately behind the head.

Tenth Family—Pristiophoridæ.

The rostral cartilage is produced, into an exceedingly long, flat lamina, armed along each edge with a series of teeth (saw).

These Sharks resemble so much the common Saw-fishes as to be easily confounded with them, but their gill-openings are lateral, and not inferior. They are also much smaller in size, and a pair of long tentacles are inserted at the lower side of the saw. The four species known (Pristiophorus) occur in the Australian and Japanese seas.

Squaloraja, from the Lias, is supposed to have its nearest affinities to this family.

B. Batoidei—Rays.

In the typical Rays the body is excessively depressed, and forms, with the expanded pectoral fins, a circular or sub-rhomboidal disk, of which the slender tail appears as a more or less long appendage. In the two families which we shall place first (Pristidæ and Rhinobatidæ), the general habit of the body still resembles that of the Sharks, but the gill-openings are ventral, as in the true Rays; the anal fin is invariably absent, and the dorsal fins, if developed, are placed on the tail. The mode of life of those fishes is quite in accordance with the form of their body. Whilst the species with a shark-like body and muscular tail swim freely through the water, and are capable of executing rapid and sustained motions, the true Rays lead a sedentary life, moving slowly on the bottom, rarely ascending to the surface. Their tail has almost entirely lost the function of an organ of locomotion, acting in some merely as a rudder. They progress solely by means of the pectoral fins, the broad and thin margins of which are set in an undulating motion, entirely identical with that of the dorsal and anal fins of the Pleuronectidæ. They are exclusively carnivorous, like the Sharks, but unable to pursue and catch rapidly-moving animals; therefore they feed chiefly on molluscous and crustaceous animals. However, the colour of their integuments assimilates so closely that of their surroundings, that other fishes approach them near enough to be captured by them. The mouth of Rays being entirely at the lower surface of the head, the prey is not directly seized with the jaws; but the fish darts over its victim so as to cover and hold it down with its body, when it is conveyed by some rapid motions to the mouth.

Rays do not descend to the same depth as Sharks; with one exception,[37] at least, none have been known to have been caught by a dredge worked in more than 100 fathoms. The majority are coast fishes, and have a comparatively limited geographical range, none extending from the northern temperate zone into the southern. However, some, if not all the species of the family Myliobatidæ, which includes the giants of this division of Plagiostomes, have a claim of being included among the Pelagic fishes, as they are frequently met with in the open ocean at a great distance from the shore. It is probable that the occurrence of such individuals in the open sea indicates the neighbourhood of some bank or other comparatively shallow locality. Many species are exclusively confined to fresh water, and occur far inland, especially in tropical America.

The majority are oviparous. All have five pairs of gill-openings. The number of known species is about the same as that of Sharks, viz. 140.

First Family—Pristidæ.

The snout is produced into an exceedingly long flat lamina, armed with a series of strong teeth along each edge (saw).